A long time ago, I had the privilege of flying in 4 engine turboprop airplanes in which the props were 'synched'(blades rotating in same speed) which of course is necessary for smooth thrust.
However, one of the exercises we performed(as a military aircraft) was called a "crash and dash"; we dove as steep as we could until we could get as close as we could to the surface, then pull out of the dive and attempt to 'fly below' any surface radar that may be tracking us.
Every time we did this maneuver it threw the props out of 'synch' and cause the airframe to shudder violently. Anything that was literally not 'nailed down' was thrown through the cockpit or cabin.
My question is, what effect does this have on the airframe and does one of the events require an inspection, or shorten the check cycle?